Paper mills have for many years made extensive use, for the cleaning of paper making stock of screening apparatus embodying a cylindrical perforated screening member defining supply and accepts chambers on the opposite sides thereof in a closed housing, and including a rotor member which operates in one of the chambers to keep the screening perforations open and free from solid material tending to cling to the screening surface. The stock or furnish to be screened is delivered to the supply chamber adjacent one end of the screening cylinder, and the material rejected by the screening cylinder is collected and discharged from the opposite end of the supply chamber.
The assignee of this invention has manufactured and sold many such screens in accordance with a series of U.S. patents, commencing with Staege No. 2,347,716, and followed by Martindale No. 2,835,173 and numerous other patents including Seifert Nos. 3,849,302 and 4,105,543. Starting with the construction shown in the Martindale patent, all such screens manufactured and sold by applicant's assignee have been characterized by a rotor which included bars or vanes of airfoil section moving in closely spaced but noncontacting relation with the surface of the screening cylinder for the purpose of creating alternating positive and negative pressure waves or pulses effective on the perforations in the screening cylinder to prevent plugging thereof.
The art has experimented to a considerable extent with detailed variations in screens of the above type, including variations in the vane shape and other forms of rotor, some such variations being shown in Seifert-Chupka U.S. Pat. No. 3,970,548, Chupka-Seifert U.S. Pat. No. 4,328,096 and Chupka et al U.S. Pat. No. 4,663,030. In general, the vaned rotors marketed by applicant's assignee have included vanes of substantially the same airfoil configuration as viewed in a section taken radially of the rotor axis.